docs: def set_var(var, set_='""'):
      '''set var outside notebook'''
      if isinstance(set_, str):
          to_set = json.dumps(set_)
      elif isinstance(set_, dict) or isinstance(set_, list):
          try:
              to_set = json.dumps(set_)
          except ValueError:
              raise Exception('var not jsonable')
      else:
          raise Exception('var must be jsonable list or dict')
  
      os.environ['NBCONVERT_' + var] = to_set